The present invention relates to bottom-opening hopper vehicles, and particularly railway freight hopper cars. The invention specifically relates to latching means for the hopper doors of such a hopper vehicle.
The present invention is an improvement of the door latch mechanism disclosed in U.S. Pat. No. 3,931,768, assigned to the assignee of the present invention, the disclosure of which patent is incorporated herein by reference. The door latch mechanism disclosed in that patent is a spring-loaded toggle device. The spring force is intended to keep the door latch in the latching configuration when the door is closed and in the unlatching configuration when the door is open. An air cylinder powers both the door and the door latch mechanism.
Thus, to unlatch the door, the air cylinder piston extends and overpowers the latch spring. Then, the door weight, the lading weight and the cylinder force combine to open the door. In closing the door, the cylinder piston retracts, the strength of the latch spring being such that the door closes but the door latch mechanism is held in its unlatching configuration until the door is completely closed. At this point the continued force exerted by the retracting cylinder piston overpowers the latch spring and toggles it to drive the door latch to its latching configuration.
In this prior apparatus, it is imperative that the door latch be held in its unlatching configuration until the door is completely closed, otherwise the door will not properly seat. The latch spring alone holds the latch in its unlatching configuration during the door closure. Thus, a weak spring, unusually high door friction or an obstacle such as a piece of lading stuck to the door or in the path of the door might cause the latch spring to be overridden prematurely, resulting in the latch moving to its latching configuration before the door is closed. When this happens, the door latch interferes with the proper seating of the door. Increasing the latch spring force would help to alleviate this problem, but in that case a higher cylinder force and air pressure would be required to latch the door. This is disadvantageous because air pressure is normally limited by the locomotive or track side supply available. Furthermore, the criticality of the latch spring force dictates strict control of the spring quality and production assembly, adding to the costs of manufacture.